Populations 5 1 Characteristics of Populations n Three

Populations

5 -1 Characteristics of Populations n Three important characteristics of a population are its geographic distribution, density, and growth rate. Geographic distribution describes the area a population lives in n Population density is the number of individuals that live in an area n

Population Growth n Three factors affect population size: n The number of births n The number of deaths n The number of individuals that enter or leave the population

Population growth n Populations grow if more individuals are born than die in any period of time Immigration - the movement of individuals into an area, can cause a population to grow n Emigration - the movement individuals out of a population, can cause a population to decrease in size n

Exponential Growth If a population has unlimited space and food, and is protected from predators and disease, then the population size will increase exponentially n Exponential growth occurs when the individuals in a population reproduce at a constant rate. n Under ideal conditions with unlimited resources, a population will grow exponentially n

Exponential Growth n n n Bacteria reproduce by splitting in half, if the bacteria have a doubling time of 20 minutes, then within 20 minutes the 1 st bacterium with divide to produce 2 bacteria. After 20 more minutes the 2 bacteria divide to form 4. After 20 minutes 4 becomes 8, in one hour there is 64, in two more hours there is 512, in just one day the colony of bacteria will be 4, 720, 000, 000 !!!!!!

Exponential Growth n A graph of exponential growth forms a Jshaped curve

Logistic Growth n Obviously exponential growth can not continue for very long. n As resources become less available, the growth of a population slows or stops. n Logistic growth occurs when a population’s growth slows or stops following a period of exponential growth

Logistic Growth Population growth may slow or stop when birthrates and death rates occur at the same rate. n Population growth will slow when immigration decreases, and emigration increases, or both. n n Carrying capacity is the largest number of individuals of a population that a given environment can support

Logistic Growth n A graph of logistic growth forms an Sshaped curve.

5 -2 Limits to Growth n Limiting Factors n Density-Dependent Factors n Density-Independent Factors

Limiting Factor n Any factor that caused population growth to decrease. Competition n Predation n Parasitism and disease n Drought and other climate extremes n Human disturbances n

Density-dependent factors n Density-dependent factors are limiting factors that depends on population size. n n The larger the population the more it is affected Examples: competition, predation, parasitism and disease

Predator-Prey Relationship n The regulation of a population by predation

Density-independent factors n Density-independent factors affect all populations in similar ways, no matter what the size is n Examples: weather, natural disasters, seasonal cycles and certain human activities

5 -3 Human Population Growth n Just like the populations of many other organisms, the human population is increasing with time

Demography n Demography is the study of human populations n Birthrates, death rates, and the age structure of a population help predict why some countries have high growth rates while other countries grow more slowly

Demographic transition n Demographic transition a dramatic change in birth and death rates which slows a countries growth rate n Age structure diagrams are models used to predict future growth of countries

Age structure diagram n Which countries has gone through demographic transition?